Interferons are proteins whose synthesis is induced in various vertebrate cells by treatment with any of large variety of inducers. The interferons are released from the producing cells, are attached to other cells and alter various characteristics of these cells. We have been investigating the biochemical of interferon action. We are planning to work on the following problems: 1) Purification and characterization of cleavage specificity and mode of activation of a 2'-5' pppA (pA)n dependent endonuclease (RNase L). 2) Purification and characterization of a double-stranded RNA dependent protein kinase. 3) Characterization of the biochemical basis of macrophage activation by interferons. 4) Characterization of interferon receptors. 5) Characterization of genes activated by interferons. Most of these studies will be performed with mouse Ehrlich ascites tumor cells and other established mouse cell lines.